Atomic force microscopy (AFM) and other types of small-scale microscopy are well-known for taking topographical measurements of the profile of surfaces, with measurements often down to the nanometer scale. Such measurements are often used in combination with indentation testing machines to generate a profile of the indentation after it has been made, so as to generate useful data about the residual profile of the indentation. This is particularly useful in the case of scratch tests, in which an indenter is dragged across a sample surface under a constant or varying indentation force. As a result, two-dimensional data relating to the residual indentation depth can be generated, and by scanning in multiple parallel passes, three-dimensional data relating to the test can be generated.
Typically, an AFM may be provided as a bolt-on supplementary module for an indentation test apparatus, which puts a large distance between the indenter and the tip, thereby requiring large displacements of the sample so as to make a topographic measurement. However, several prior art indentation testers integrate an AFM (or similar) tip with the indenter, which serves to position the indenter and is used for measuring penetration depth, reducing this distance and thus enabling more precise referencing of the topographic measurement. For instance, U.S. Pat. No. 7,568,381 describes use of an AFM tip as part of a reference sensor, as does EP 2 816 342.
Typically, using the AFM tip to take a topographic measurement requires typical dedicated AFM sensors to be incorporated in the apparatus to make measurements with the AFM tip rather than just to detect the surface of the sample, which adds complexity and cost.
An aim of the present invention is thus to propose a method for taking topographic measurements of the surface of a sample using an indentation apparatus without having to provide further sensors other than those already provided on the indentation apparatus.